How to use different Python version in venv from standard library? (Not virtualenv!)

I have installed Python 3.4.0 and created virtual environment with

python -m venv myenv

. How can I change Python version in my virtual environment? Documentation says:

Each virtual environment has its own Python binary (allowing creation
of environments with various Python versions) and can have its own
independent set of installed Python packages in its site directories.

UPDATE

Please, note that I ask about venv from standard library, not about virtualenv.
Let me provide some links.